Parametric Optimization and Kinetics Study of Effective Removal of Methylene Blue by Citric Acid-Modified Arjun Bark Powder

The adsorptive removal of methylene blue (MB) from its aqueous solution using citric acid-modified arjun bark powder as an adsorbent was studied. Initially, the adsorbent was characterized by various analytical techniques (SEM, BET, FTIR, and pH(pzc)). After characterizing the adsorbent, it was used for carrying out batch study on the biosorption of MB. The batch experiments revealed a very high percentage removal of MB of about 100%. The batch experiment results followed Temkin isotherm. The maximum monolayer adsorption capacity observed was 512.82 mg/g at natural pH of 7.5. The Freundlich isotherm constant was found to be 300.15 l/g. The Temkin isotherm constant was found to be 21.32 l/mg. The sorption energy was calculated from the Dubinin-Radushkevich isotherm model, and it was found to be 10 kJ /mol. On the other hand, results followed the pseudo-second-order kinetic model. The energy of activation in the present study was estimated to be 10 kJ/mol. The adsorptive mass transfer coefficient was calculated to be 1.65 x 10(-7) m/s, and the value of diffusivity was found to be 2.27 x 10(-11).